Optical networks include nodes interconnected by optical links formed by fiber optic cables including various pre-amplifiers, post-amplifiers, optional intermediate line amplifiers, etc. One particular issue on optical links includes power control, namely the power on an optical link changes over time with the addition or removal of optical channels and such a process requires power control to adjust settings on the various components. There are various power control techniques utilized to control optical power over the optical links, responsive to capacity changes. With advance coherent modulation and the like, conventional power control techniques are slow, i.e., operate in seconds, leading to slow capacity changes. Speeding up such techniques can and does have a negative operational impact on existing in-service channels. A technique to deal with the control of optical power involves the use of so-called channel holders, which can include Amplified Stimulated Emission (ASE) sources, modulated lasers, unmodulated lasers, etc. Channel holders are used in optical links to keep optical spectrum in full-fill loading condition so that any capacity change activity can be digitally handled by switching the channel holders with traffic signals, i.e., there is no need to perform an optimization because any capacity change includes swapping a traffic-bearing channel for a channel holder or vice versa. That is, the power optimization only needs to be performed at turn-up when the timing does not impact the operation. Once the power is optimized, capacity changes are just swapping channels for channel holders or vice versa. This is more of a digital operation, whereas conventional power control techniques are more of an analog operation. That is, swapping an optical channel for a channel holder or vice versa can be performed much quicker than any conventional power control technique.
In addition to the movement towards channel-holder based optical links, there are also emerging techniques to better manage the optical spectrum usage, including flexible grid approaches, super channels (supercarriers), etc. For example, details of these optical spectrum techniques are described in commonly-assigned U.S. Pat. No. 10,200,770, issued Feb. 5, 2019, and entitled “Management of flexible grid and supercarriers in optical networks using a data model,” the contents of which are incorporated by reference herein. As described herein, a Network Media Channel (NMC) is the bandwidth corresponding to the spectral width of an optical signal and a Media Channel (MC) is the spectral allocation in the medium which encompasses one or more NMCs and any imposed excess spectrum for optical filter penalties (e.g., filter roll-off), excess spectrum for future growth, etc. Multiple NMCs that support a single digital carrier are known as a supercarrier. A Media Channel can also be referred to as a super channel. Additional details are described in ITU-T Recommendation G.872 “Architecture of optical transport networks,” (January 2017), the contents of which are incorporated by reference herein.
Media Channels can include a wide range of the optical spectrum that may be initially provisioned, but a Media Channel may not have actual NMCs configured therein. Of course, this eliminates many of the benefits of the channel-holder based approach. Thus, there is a need for supporting channel holders within intended Media Channels in spectral locations, where expected NMCs may not be provisioned yet, or deployed NMCs could be faulted due to loss of power.